One of the biggest reasons for many people to switch to a UNIX desktop, away from Windows, is security. It is fairly common knowledge that UNIX-like systems are more secure than Windows. Whether this is true or not will not be up for debate in this short editorial; I will simply assume UNIX-like systems are more secure, for the sake of argument. However, how much is that increased security really worth for an average home user, when you break it down? According to me, fairly little. Here's why.

Probably through some application (especially media program) that has some buffer overflow exploit that allows remote execution of code. Either that, or social engineering.

That second one is the one to be most concerned about. In order for Linux to work for the masses, it has to be easy to install and run applications. And once that is possible (it probably is already) and you put Joe Sixpack on it, all I gotta do is send him an email promising him nude pics of J-Lo and all he has to do is execute this file. And presto .. you've got an epidemic on your hands.

Of course, Unix/Linux is more secure than Windows. But keeping a Windows box secure isn't that complicated, as I've said before. If I could spend about 30 minutes with each and every Windows user and install Firefox or Opera for them, Windows security issues would be pretty much non-existant.

You can send Joe Sixpack an email with malware on it. It will not run. It has been said before over and over, there will be no execution rights on attachments.
Social engineering would work of course, you can get some dopeydick to type rm -f * as root with silly promises, but that is not a fault of the system.....

There is a fundemental difference between Windows and Linux.
Around 1994 Bill Gates & Co. decided that making everything automatic was good for the user. this is the root cause of all the problems with Windows.
You can spend all the time in the world with Windows users, and convert them to Opera and Firefox all you want, however, the problem is just not with the browser.
Windows has problems with email, messengers, browsers and media players, all having access to the system areas and all being able to interoperate with each other.

People do live with their head in the sand. Windows can never be secure if Microsoft are trying to make it as easy to use as possible. Linux and Unix are ultimately more secure because they have been designed with security in mind from the ground up.